Question

A parallel-sided plate of glass having a refractive index of 1.58
is in contact with the surface of water in a tank. A ray coming
from above makes an angle of incidence of 31.2 degrees with the top
surface of the glass.

What angle does this ray make with the normal in the water?

Could you please show me the formula and steps for how you came up
with the answer?! Thank you! :)